1. Field of the Invention
This invention relates to a GaP light emitting element substrate, and more specifically to a GaP light emitting element substrate comprising a substrate with a plurality of GaP layers on it which is used when manufacturing GaP light emitting diodes which emit green light.
2. Prior Art
Light emitting elements such as light emitting diodes are normally obtained by layering a plurality of semiconductor layers on a semiconductor substrate to prepare a multi-layer semiconductor substrate with a pn junction(s), and making this into elements. Of these, green light emitting diodes can be obtained by using a light emitting element substrate prepared by forming one or more layers of both n-type and p-type GaP layers, one after another, on an n-type GaP single crystal substrate.
GaP is an indirect transition type semiconductor, ant therefore the brightness is very low when a pn junction is simply formed. Therefore nitrogen (N), which would be the luminescence center, is added to the n-type GaP layer in the proximity of the pn junction to increase the light emitting output. A light emitting diode prepared from the GaP light emitting element substrate which has the nitrogen-doped n-type GaP layer, as described above, will produce a yellow-green light emission with a peak wavelength of about 567 nm.
Recently, the progress of GaP light emitting diodes which emit green light has been remarkable, and each year diodes with higher light emission outputs are developed. Along with this trend toward higher light emission output, the application range of the GaP light emitting diodes has spread to a very wide range. However, development of light emitting diodes with even higher light emission outputs is desirable in order to further expand the application range.
However, there is a problem which constitutes an obstacle when designing GaP light emitting diodes with higher brightness. The problem lies in that the brightness of the light emitting diodes varies significantly depending on the manufacturing lot of the buffer layer of the GaP light emitting element which is used in manufacturing the GaP light emitting diodes, and that sufficient brightness may not be achieved depending on the manufacturing lot.
Although the buffer layer does not directly contribute to the light emission of a light emitting diode, it seems that the quality of the buffer layer has some kind of influence on the brightness of the light emitting diode. Therefore, the brightness of the light emitting diodes is expected to improve by improving the quality of the buffer layer.
Therefore, the object of this invention is to provide a GaP light emitting substrate which allows manufacturing of GaP light emitting diodes with less dispersion of the brightness depending on the manufacturing lot of the buffer layer as well as with high brightness.